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Question
If 3x + 2y = 9 and xy = 3, find : 27x3 + 8y3.
Sum
Solution
27x3 + 8y3 = (3x)3 + (2y)3
= (3x + 2y)3 − 3.3x . 2y (3x + 2y)
= (3x − 2y)3 − 18xy (3x + 2y)
= (9)3 − 18(3) (9)
= 729 − 486
= 243
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